Numerous schemes have been proposed for apparatus using adaptive quantization techniques. See, for example, the article entitled "Adaptive Quantization in Differential PCM Coding of Speech" authored by P. Cummiskey, N. S. Jayant and J. L. Flanagan, Bell System Technical Journal, Vol. 52, September 1973, pp. 1105-1118, hereinafter referred to as the B.S.T.J. article. Such schemes have in common the objective of continually tracking changes in signal power level. As a consequence, even if the signal power level happens to remain constant, the quantizer decision levels fluctuate randomly according to short-term estimates of the current power level and thus the quantizer characteristic is constantly being altered. Ideally, a quantizer for a given constant signal power level should have a constant characteristic matched to that power level.